1. Field of the Invention
The present invention relates to a spectral distribution measuring device which measures a spectral reflection distribution in an arbitrary position of an image printed on a surface of an image forming medium such as paper.
2. Description of the Related Art
Many image forming apparatuses such as a printer, a copier, a high-value-added complex machine and a commercial printing machine in which a communication function is added to a printer and a copier are available on the market. As a method of forming an image adapted to these image forming apparatuses, various methods are known such as an electrophotographic method, an ink jet method and a thermosensitive method. In the commercial printing field, a sheet-fed press and a continuous printing machine are increasingly becoming digitized, and many products utilizing an electrophotographic method and an ink jet method are being introduced are brought into the market.
By the fine development and the colorization of an image which is handled in these image forming apparatuses, a picture, a catalogue and an invoice can be printed at a high quality according to a personal preference. In the commercial printing field, with the fine development and the colorization of a printed image, services which are provided to consumers by advertisements have been diversified. In order to secure the accuracy of information which is provided by such services, it is necessary to secure image quality accuracy such as color reproducibility.
As a technique which secures such image quality accuracy, an electrophtographic image forming apparatus, which has a concentration sensor for detecting the concentration of toner adhered onto an intermediate transfer body and a photoreceptor before being fused, and stabilizes the amount of toner on a surface of a print by controlling the amount of toner to be supplied according to the detection result, is available on the market.
As a technique which secures accuracy of information such as personal information, an image forming apparatus which inspects a printed result is available on the market. In such an image forming apparatus, despite an image forming method, for example, a printed image is imaged by an imaging element so as to be recorded as image data, the characters of the original image and the printed image are recognized and compared by using a character recognition technique, and a difference between those images is detected by the difference between these image data.
Moreover, as a technique which secures color reproducibility, for example, an image forming apparatus, which prints a color patch for inspection on a surface of a print, measures it by a spectrometer, compares the measured value of this color and the color data of the color patch, and performs calibration according to the difference, is available on the market.
These techniques aim to control image quality fluctuation among a plurality of pages or on one page, so it is preferable to perform measurement of a spectral reflection distribution of a print with respect to an entire area of an image.
As one example of a measuring device which measures a spectral reflection distribution with respect to an entire area of an image of a print, a measuring device described in JP2008-518218A includes a plurality of scanning units to an object being measured (hereinafter, measuring object), which measures spectral reflectivity of wavelength bands different to each scanning unit.
By using these scanning units, spectral reflectivity at arbitrary points on an image of a measuring object is simultaneously measured at different wavelength bands, and colors in respective points on the image are measured over the entire area of the image.
A measuring device described in JP2005-315883A includes a scanning unit having a LED array light source in which a plurality of LEDs each having a different color is arranged. The measuring device is configured to sequentially illuminate the LED array of each color when the measuring object and the scanning unit are relatively moved, measure the reflection light from the surface of the measuring object by the illumination of different colors and estimate the spectral distribution from the measurement data.
In the measuring device of JP2008-518218A, however, when relatively moving the measuring object and a plurality of scanning units, for example, if the measuring object meanders or is inclined to a plurality of scanning units, the measuring object is displaced to each scanning unit, and it becomes difficult to align images among respective image data measured by respective scanning units. For this reason, it becomes difficult to measure the colors of the measuring object with a high accuracy.
In the measuring device of JP2005-315883A, the relative positional relationship between the measuring object and the scanning unit differs with respect to each color to be illuminated by the mistiming of the light emission of the light source of each color in scanning. For this reason, the light reflected from the different positions of the surface of the measuring object is measured by a line sensor. Therefore, color data to the same point of the measuring object can not be measured, so that it is difficult to measure the colors of the measuring object with high accuracy.